1. Field of the Invention
The present invention pertains to methods and apparatus for cutting tubular members, such as pipe members. More particularly, the present invention relates to techniques for cutting tubular members, particularly metal pipe, from the inside using explosive charges. Such techniques find particular application in cutting pipe members positioned at remote or inaccessible locations, such as within wells, where the use of conventional pipe cutting practices is prohibited.
2. Description of Prior Art
In operations on wells, particularly deep wells as are known in the oil and gas industry, occasionally pipe members situated downhole must be severed or cut loose. Such occasions arise, for example, when drill strings or drill collars become stuck in the well and cannot be retrieved.
It is known to sever such stuck drill collars or drill string at a desired location in the well by using an explosive cutting device. Such a tool is lowered into the well, usually on a wireline, and positioned at the location where the tube cut is to be made. To assist in placing the explosive device at the correct position, a locator may be lowered with the cutting device to locate the pipe member to be cut. An electric detonator within the explosive device is initiated by an electric signal from equipment at the surface, and in turn initiates a fuse which detonates a high explosive charge. The shock effect from the high explosive charge breaks up the surrounding tubing in the vicinity of the explosion, thereby severing the tube.
In view of the danger inherent in the use of high explosives, particularly in oil and gas wells, it is desirable to effect the cutting of such tubing with maximized efficiency, utilizing the minimum amount of explosive charge necessary. Additionally, it is desirable to leave the well after the cutting of the tubing with as little debris as possible. For example, if the portion of the tubing remaining in the well after the cutting operation includes segments that are twisted and bent to obstruct the central passage in the well, such material may prevent further operations in the well until the obstructions are cleared. Consequently, it is advantageous to provide a tube cutting technique which makes as clean and neat a cut in the tubing as possible.